1. Field of the Invention
The present invention relates to a sensor-enabled geosynthetic material used to construct geosynthetic structures (i.e. geotechnical structures involving geosynthetics) and a method of making the sensor-enabled geosynthetic material. Additionally, the mechanical strains of the sensor-enabled geosynthetic material can be measured or monitored without the need for conventional instrumentation.
2. Description of the Related Art
Geosynthetics are polymer-based products specifically manufactured to serve a wide range of applications in civil and environmental engineering including soil stabilization and reinforcement, separation and filtration, drainage and containment. The emergence and development of geosynthetic technology has had a significant impact on the capabilities and economics of civil engineering design and construction. Increasing number of geotechnical projects involve the applications of geosynthetics as modern solutions to conventional problems with proven advantages in the construction and retrofitting of infrastructure including: ease and speed of construction, construction in difficult access locations, superior performance under static and seismic loading conditions, lower costs, reducing the size of structures and hence providing greater usable space, aesthetically pleasing appearance and blending with the environment. In several cases (e.g. geomembranes in hazardous and municipal waste containment), the use of geosynthetics is mandated by law.
Geosynthetic engineering and the related manufacturing and construction industries have experienced tremendous growth over the past few decades and are now an established technology involving billions of dollars of projects in the U.S. and worldwide. At the same time, as geosynthetic-related structures and facilities become ubiquitous, it becomes vital to ensure that these structures are not only safe but also offer a satisfactory level of serviceability through health monitoring and timely measures to prevent catastrophic failures and costly repairs due to inadequate structural performance resulting from uncertainties in site conditions, material properties and behavior, construction practice, environmental effects and loading conditions. This is especially true where these structures support crucial infrastructure in urban areas and along transportation corridors, or protect the environment from hazardous waste, leaking fuel or other contaminants. The importance of instrumentation and health monitoring of infrastructure is increasingly recognized in order to address these challenges and uncertainties to ensure the success of the project with respect to its safety and cost. An important aspect of health monitoring for geosynthetic structures is to monitor geosynthetic strain during service life and/or extreme (e.g. seismic) events.
Geosynthetics have become an indispensable part of the infrastructure development and renewal enterprise. Unfortunately, a vital aspect of sustainable development; namely, their instrumentation and health monitoring has received comparatively little attention with costly consequences. A significant predicament in performance monitoring of geosynthetic structures has been due to the fact that installation of instruments (e.g. strain gauges) are typically tedious and costly with rather unpredictable outcome. Current design guidelines for different geosynthetic structures are largely based on empirical and conventional (e.g. limit-equilibrium) approaches without proper assessment and in-depth understanding of the influence of important factors such as peak strain and in-soil properties of geosynthetics. As a result, overly conservative design procedures and reduction factors are typically imposed on the strength of the geosynthetic material to address concerns related to their durability and creep. This renders the cost of these structures in many instances much greater than necessary, and counters their intrinsic cost-effectiveness. Other important applications which could benefit significantly from a reliable health monitoring system include landfills to detect geomembrane overstress at their trenched anchors, covers or other locations (e.g. within geomembranes often buried under hundreds of feet of waste) well before the occurrence of leakage under service conditions or, e.g. following seismic events. Current technology merely involves leak detection systems which could only detect the problems in more advanced stages. Similar benefits could be achieved in geopipes, geosynthetic platforms over sinkholes and other soil stabilization, containment and storage applications.
In addition, the existing technology currently employed to measure strains in geosynthetics requires complex and expensive data acquisition systems. The existing technology for the instrumentation of geosynthetics primarily entails the attachment of strain gauges and extensometers to a geosynthetic material which are calibrated against average strains from crosshead displacement in their in-isolation tests. However, these calibration factors are not truly applicable to a geosynthetic layer embedded in soil due to at least three important reasons: 1) different in-soil mechanical properties (e.g. tensile modulus) of geosynthetics compared to their in-isolation values due to confining pressure and interlocking effects, 2) complications such as soil arching due to the mechanical interference and interaction of strain gauges and their bonding assembly (e.g. adhesive and protective sleeve) with the local soil, 3) unknown local stiffening effect of the bonding assembly. These factors can introduce significant errors in measured strains in geosynthetics in field applications. Applying in-isolation calibration factors to in-soil readout data could lead to significant underestimation of reinforcement strain and axial load with potential consequences with respect to stability and performance. Recent studies include discussions on subjects such as strain gauge calibration, local vs. global strains, under-registration of strain due to attachment technique and correction factors to estimate global strains in geosynthetic reinforcement.
In addition, geosynthetic strain is not routinely monitored in the field due to the added costs and level of care and skills required for proper installation of the instruments. Other impediments include lack of reliable strain gauging techniques and proper training of contractors, durability and reliability of instruments and requirements for time-consuming installation and protection measures. For these reasons, geosynthetic instrumentation in the field has been primarily limited to research and demonstration projects with a comparatively insignificant footprint in their mainstream construction considering the vast number of geosynthetic-related structures constructed in the U.S. In those occasions where field structures have been instrumented, the extent of instrumentation related to the geosynthetic strain data has been fairly limited. As a result, important information on the extent and distribution of strains and stresses in these structures is not typically available.
Recent attempts to measure soil strains and in-soil reinforcement strains include those involving digital imaging, X-ray and tomographical techniques in small-scale laboratory specimens. However, the limited in-soil penetration range of these techniques renders them impractical for field-scale structures. Another recent development involves the attachment of fiber optic cables to geotextiles or geomembranes. However, these techniques do not incorporate the sensing capabilities within the geosynthetic materials, and the added manufacturing and construction costs related to the fiber optic material and their installation need further analysis.
Accordingly, there remains a need for a new generation of geosynthetics having sensing capabilities embedded therein in order to measure their mechanical strain without the need for conventional instrumentation.